1. Field of the Invention
The present invention relates to a method of forming a microscopic opening serving as a near field light generating device by a photolithographic technique using illumination light.
2. Description of the Background Art
In conventional optical recording, a recording density has an upper limit determined by the diffraction limit (which means that the size of a spot focused by diffraction of light is not infinitesimal), and hence only marks having a size on the order of magnitude of the wavelength of light (hundreds of nanometers) can be read or written.
In recent years, a technique which utilizes near field light (evanescent light) to increase the recording density in optical recording has attracted particular attention. A recording method which utilizes the near field light makes it possible to read marks as small as tens of nanometers in size beyond the diffraction limit of light by reducing a spacing between an optical head and a recording medium down to tens of nanometers. On similar principles, it also becomes possible to form microscopic patterns beyond the diffraction limit by using the near field light.
In these techniques using the near field light, an optical probe is desired which can form a microscopic light spot with as high an intensity as possible. To this end, there has been proposed a fiber probe having an opening at a sharp-pointed tip of a fiber. However, the size of the opening of a probe on the order of 100 nm causes an extremely low intensity of transmitted light, for example, on the order of 1/100 or below, resulting in low efficiency of use of light.
To overcome this problem, a technique has been proposed which produces a tapered microscopic opening by anisotropically etching a thin film of single crystalline silicon and directs light into the microscopic opening to generate near field light from the microscopic opening (as disclosed in U.S. Pat. No. 5,689,480).
Unfortunately, the technique disclosed in U.S. Pat. No, 5,689,480, in which etching is used to produce the tapered microscopic opening, has poor reproducibility of the microscopic opening, presenting difficulties in maintaining good product quality. This technique also requires precise control of etching time, resulting in low yields.